Preventive Maintenance of HT Panel

Objective

This post describes safe, methodical, and logical HT Panel PM preventive maintenance steps.

Scope

This SOP recommends facility operation and maintenance improvements with explanations.

Abbreviations

• SMP – Standard Maintenance Procedure
• SIC – Shift In Charge
• EE – Electrical Engineer
• ST. Mg – Station Manager 
• HOM – Head of Maintenance
• HOO – Operation Head

Responsibility

• Station Manager, 
• Head of Operations, 
• Head of Maintenance, 
• Maintenance Engineer, 
• Shift Supervisor

OHS (Occupational Health and Safety) Risk

• Electrical burn 
• Cut 
• Electrical shock

Cautions & Special Safety Precautions

• Double check that the workers are wearing the necessary personal protective equipment 
• The visitor should not move in close proximity to the work area.
• Ensure that the area is kept clean and the obstructions are removed. 
• Do not wear gloves of the wrong size.
• In the barricaded area, you should not enter.
• While the contacts on the breaker are closed (or) the closing springs are being charged, it is important to keep your hands and fingers away from the internal portions of the breaker. 
• It is possible for the contacts of the breaker to open or for the closing springs to discharge, which would result in crushing injuries. 
• Before operating on the breaker, it is necessary to discharge the charged springs by performing one action that involves closing and tripping the circuit.
• Prior to starting maintenance, warning signs are required to be positioned at the switchboard first.
• In order to carry out the maintenance, the HT breaker must be turned off, racked out, and placed correctly on the trolley.

Special Personal Safety PPE’s Protection

• A Protective Helmet
• A pair of Safety Shoes
• Electric Hand Gloves
• Eye Protection Goggles
• Rubber Mats
• Dust Mask

Environmental Protection

• Store waste cardboard and packing materials in nearby dust bins & dispose of them according to the waste management plan.
• Dispose of empty aerosol cans according to the waste management strategy.
• Used cotton waste should be deposited in nearby dust bins & incinerated.
• Collect and dispose of generated garbage, including used cables, insulation material, and spares, according to the waste management approach.

Maintenance Procedures

Busbar and Cable Chamber Maintenance

• Isolate and discharge panels before commencing the job. 
• Measure the insulation resistance of incoming cable & bus separately.
• Inspect insulation on any outbound feeder cables & wiring.
• Check the bus bar’s support insulators for cracks, deformation, color changes, stresses, and foreign material.
• Any insulation maintenance essentially entails keeping all insulating surface clean.  This can be accomplished by wiping down insulating surfaces with a dry, lint-free cloth or paper towel.  
• Clean the collected dust (or) moisture on epoxy resin post insulators with a soft, dry cloth, and refresh as needed.
• To remove stubborn dirt, use a mild solvent (or) distilled water if wiping is ineffective. However, before using the surfaces, ensure that they are completely dry.
• Inspect contacts and remove any dust deposits. If the contact surfaces are rough, treat them with fine emery paper. Use a thin layer of petroleum jelly as needed.
• Ensure mounting screws & nuts are tight & connections are properly aligned.
• Check insulators for tightness. Do not put additional stress on the insulators. (They may crack.)
• Inspect bus bars and chambers for wear and damage. Clean as needed with plate polish. Check the bus bar’s connecting bolts for tightness.
• Inspect wiring & terminations for discoloration from heat, exposed conductors, and loose connections.
• Inspect control & power cabling terminations for discoloration from heat scorched or exposed conductors, and loose connections.
• Ensure air vents are not clogged.
• Check CT scans for any abnormalities.
• Ensure CT secondary neutrals are properly earthed.
• Determine the IR and continuity of the anti-condensation (space) heater. The resistance of space heaters must fall within the limits provided by the vendor.
• Verify the earth connections for safety & tightness.
• Use a 2500V megger to measure & record insulation values for each panel’s bus bar & out-going cables.

Breaker and Meter Compartment Maintenance

• Inspect switches for proper operation and internal components, including fuses and terminals.
• Check fuse connections for tightness and correct rating. Renew the fuse as needed. 
• Inspect control fuses for CTs and PTs. Check the fuse holder for overheating and ensure that the fuses are of the correct rating.
• Clean dust from panel and verify for proper sealing. 
• Ensure each circuit labels are appropriately connected to their respective panels.
• Inspect and test the draw-out mechanism, lubricate as needed, and ensure smooth operation.
• Inspect and test the safety shutters mechanism to ensure smooth & proper operation.
• Inspect breaker wiring for evidence of overheating and damage. 
• Ensure that every connection are tight and secure.
• Check the Line and Bus -PTs for any abnormalities. 
• Earth the secondary neutrals of Line and Bus-PTs.
• Inspect, clean, and test all auxiliary devices, including relays, contacts, and control transformers.
• Inspect the breaker and panel mounted limit switches.
• Check & clean earth & auxiliary contacts. Check that all connections are tight and secure.
• Measure insulation. Resistance of the main and control circuits.
• Ensure proper operation of all indication flags and lamps.
• Clean and lubricate all door hinges and locks.
• Manually operate protection devices and monitor for tripped breakers.

HT Panel Maintenance 

• Clean the panel both within and externally.
• Check control and power connections for tightness.
• Inspect lugs and cables for signs of overheating.
• Ensure tightness of the main busbar & coupler.  
• Examine earthing for tightness.
• Ensure the panel is vermin-proof.
• Inspect heater and thermostat performance.
• Check ON/OFF and emergency push buttons. 
• Use a 5 KV Megger to measure the I.R. value of the bus bar. (Phase to Earth & Phase to Phase) Before removing the Bus and Line PT/PT fuses. 
• After Meggering, insert the PT/PT fuses. 
• Test the electrical ON/OFF & spring charging of the breaker at the TEST position.
• Test the mechanical on-off & spring charging of the breaker at the TEST position.

Documentation

The values of all the testing parameters should be recorded, and the entry should be made in the check sheet.

Reference 

S.No	Document Name	Document Number
1.	O & M Manual
2.
3.
4.
5.

Records

S.No	Record	Record  Reference Number	Record  Location	Retention Time
1	Logbook
2	Register  History
3	Preventative Maintenance Schedule
4	Monthly Report
5	Annual Report